There are various known means to generate electromagnetic power. For example, most generators are built with a radial flux configuration. This means that the air gap between the stator and the rotor is cylindrical. In permanent magnet generators, often the permanent magnets rotate and are located in the interior, while the coils are stationary and located on the exterior.
The chief advantage of this kind of generator is that because of its ubiquity, there are a large variety of off the shelf systems in many configurations. However, they tend to be longer than they are wide in diameter, and most are not very efficient below 1000 RPM. This makes them difficult to package in a wheel and use in a direct drive configuration at common driving speeds.
Further, there are several consumer products on the market such as flashlights that generate power via a linear motion, induced by acceleration or tilt. The wheel is constantly rotating through the gravitational field, so it is possible to use such a scheme to generate electrical power.
However, a large sports utility vehicle (SUV) wheel at 25 mph results in a centripetal acceleration of about 10 g at 130 mm (about 5 in) from the axis. This means that if a mass were allowed to move freely in the radial direction, the centripetal force would overwhelm the 1 G gravitational acceleration, resulting in the mass moving to the outermost position of the rim and staying there.
However, although the gravitational acceleration is overwhelmed by the centripetal acceleration, there is still a 10% variation in the inertial forces on a mass at this location, which could be used to generate power. One technique would be to attach the mass to a spring attached in the radial direction, and use the resulting motion to drive an electric machine. However, it would be difficult to get a very large motion, making it very difficult to harness significant electrical power this way.
In the past two decades, reasonably priced high remanence magnetic materials such as Neodymium-Iron-Boron (Nd—Fe—B) have become available, enabling new electric machine configurations. One of these is the axial flux permanent magnet machine, which has an air gap shaped like a circular face. These machines have seen many applications as generators, especially in small-scale wind power.
Several rear projection technologies are commercially available. Each of the three primary technologies—Liquid Crystal Display (LCD), Digital Light Processing (DLP), and Liquid Crystal on Silicon (LCOS) depend on a very bright white light source and blocking spatial and color components of the light beam to produce an image. Even though the light source may be very efficient, overall efficiency is reduced because light is blocked/absorbed to create the image.
A Liquid Crystal Display (LCD) creates an image by aligning liquid crystal molecules to block or transmit light. LCD displays may be back lit-having a light source located behind the display, reflective—using impending light, or transflective—combining the two strategies. It is difficult to achieve both power efficient daylight readability and nighttime readability in the same display. However, nearly all LCDs are manufactured to have a rectangular form factor, which can be difficult to apply to a circular wheel face.
Bistable displays have pixels whose states are electrically set, but which maintain the set state without the application of power. These displays use little power, but cannot display video, and are not visible without external lighting.
Therefore, there is a need to develop an auxiliary electrical power source from an inter-wheel generator and a visual display of information, visual images and full motion video sequences on the rotating wheels of a vehicle.